1. Field of the Invention
The present invention relates in general to an automatic air pump that has merits of low cost and quick inflation.
2. Description of the Related Art
As shown in FIG. 1, an automatic air pump (8) of the prior art has a pump body (81) with a spring (82) received inside. The pump body (81) is made of flexible material, such as PVC, and can be flattened.
While operating the air pump (8), the user depresses it to discharge the air inside, through an air outlet (86). The pump body (81) is flattened and the spring (82) is compressed. Then, the user releases the air pump (8), restoring the pump body (81) automatically to its original shape under the action of the spring (82). Also, outside air is sucked into the air pump (8) through an air inlet (85). By repeating the above operations, the air pump (8) can continuously supply air.
Check valves (83) and (84) are necessarily provided in the air inlet (85) and air outlet (86) to control the direction of the airflow. It is understood that various kinds of check valves can be used.
However, a pump body (81) made of flexible material is easily punctured by the spring (82) which is generally made of steel. Furthermore, the air pump (8) cannot readily be packaged for sale and transport.
To solve the foregoing problem, U.S. Pat. No. 4,930,174 discloses an automatic air pump in which foam is received. The foam has many pores itself and is elastic. When the user depresses the air pump, both the foam and the pump body are flattened. The air contained in the pores of the foam is squeezed out, then into an air mattress (i.e. the air mattress is pumped). When the user releases the air pump, the foam regains its original shape due to its own elasticity and absorbs outside air through an air inlet.
In such a case, however, the foam in the air pump cannot contain too much air. Therefore, it takes many pumping operations to fill the air mattress with air. Another similar case is disclosed in Germany Patent DE 4034593 A1.